The present invention relates generally to a method of operating hydraulically-actuated fuel injection systems and, more particularly to a method of tuning each hydraulically-actuated fuel injector within the hydraulically-actuated fuel injection system.
Hydraulically-actuated fuel injection systems typically utilize an electronic control module to control the timing and the quantity of fuel injected into the engine. One function of the electronic control module is to store optimum fuel injection system operating parameters. This stored information relates to performance of a theoretical, nominal injector. Because performance of actual fuel injectors rarely conforms to the standards of the nominal injector, it is desirable to alter the actual operating conditions of the fuel injection system to correct for the performance of the actual fuel injectors. FIG. 4 shows an example of a nominal fuel injector trace compared to that of one actual fuel injector at one operating condition. In this example, the actual fuel injector differs from the nominal injector in both start of the injection (SOI) and in the mass quantity of fuel injected, which relates to the duration of the injection event. This actual injector could be made to perform more like the nominal injector if the SOI and the on-time were both adjusted. The present invention is directed to adjusting only the on-time of the injector and not the SOI.
This alteration could be made as a function of the average fuel consumed by all fuel injectors operating in a fuel injection system. After a fuel injector is manufactured, and prior to its installation in an engine, a single spray test is performed at one operating condition to measure a test volume of fuel injected by the fuel injector. An acceptable range of results is predetermined by expected performance of a nominal injector at that condition. If the result of the spray test for a fuel injector falls within the acceptable range, the result is recorded and the fuel injector is marked with a serial number. If the result of the spray test falls outside of the acceptable range, the fuel injector is rejected.
When the accepted fuel injectors are installed into the fuel injection system, a system-wide adjustment could be instituted based on a comparison of actual fuel consumed and expected fuel consumed. The total volume of fuel that should have been injected is determined based on a fuel injection system including nominal fuel injectors. For example, if the fuel injection system includes six fuel injectors, the nominal volume is calculated by adding up the predicted volume consumed by six nominal fuel injectors. A comparison of the actual volume consumed with the nominal volume is used to calculate a single on-time adjustment that is applied to all fuel injectors in the system. Because all fuel injectors are now made to operate at a level determined from their average performance, some injectors are going to perform better than before the correction, but others are going to perform worse. While the engine with such an average correction will perform overall closer to nominal expectations, engine vibration, noise and emissions may not be reduced because not all fuel injectors are performing at a better level. In one or more cases, the engine vibration, noise or emissions might actually increase.
An occasional increase in some of the undesirable engine outputs is an indication that a particular method of adjusting the on-time of fuel injectors fails to acknowledge that all fuel injectors perform differently with respect to each other. Engineers have observed that not only do fuel injectors behave differently with respect to each other, but that an individual fuel injector may also behave differently at different operating conditions. Therefore, while an average adjustment may enable the fuel injection system to perform better at one operating condition, the fuel injection system might in fact perform worse at a different operating condition.
The present invention is directed to overcoming one or more of the problems set forth above and to improving the performance of hydraulically-actuated fuel injection systems.
A method of tuning a hydraulically-actuated fuel injection system, which includes at least one hydraulically-actuated fuel injector, requires performance of at least two tests on each fuel injector. These tests are performed at a first condition and a second condition, and the results for each test are recorded. The recorded results are then compared to the expected results of a nominal injector at the same conditions. If this comparison yields a difference between the fuel injector and the nominal injector, the on-time for the fuel injector is adjusted accordingly.